DESCRIPTION (adapted from applicant's Description): Youth-onset, insulin- dependent diabetes mellitus (IDDM) is one of the most important, if not the most important chronic disease of children in the United States. It is a disease that has been labeled as the geneticist's nightmare. In contrast, it is the epidemiologist's dream disease, in that it is much easier to investigate epidemiologically than practically any communicable or non-communicable disease. IDDM is ideally suited for registries, for poor as well as rich countries., especially since the children can be easily identified. A major component of IDDM is the extraordinary dynamic nature of the disorder, in that one can found enormous geographic variation. Currently, there are 300-fold differences in incidence, by nation, and clear spiking incidence patterns over time. The latter are reminiscent of classical epidemics and extremely strong risk markers. The application posits that much of the riddle of IDDM can be resolved in China. The incidence of IDDM in China is 1/150-1/40, with clear evidence of epidemics. Although Chinese children have a low risk for disease, epidemics do occur; a better understanding of those observations could provide potentially important information about the pathology of IDDM and could also contribute to the body of knowledge about the increased risk for minority children in the U.S. Data will be collected to address: 1) whether there is an association, either geographically or temporally, between reported infections and IDDM in China; and 2) whether there is evidence for factors which precipitate IDDM in China. In order to test these hypothesis, the IDDM monitoring, already underway in China, will be expanded from 20 million to 43 million children. The excellent, systematic disease reporting system in China will be used to compare the incidence of IDDM to past infectious diseases.